Biodiversity is the variety observed in organisms at every level of biological organization. As ecologists studied biodiversity in the environment, they observed a regular pattern in which diversity was distributed over the entire area of the planet. Ecologists discovered two broad kinds of diversity patterns, namely:
- Latitudinal gradient – This is the most well defined and well-known pattern of biodiversity studies till date. According to this pattern, the species diversity follows a regular pattern as we move from the equator to the polar regions. The plant and animal diversity observed to be maximum at the equator and it decreases as we move towards the poles. There might be an exception of a few species, but apart from that, it is a generally observed trend. We find species richness in plants and animals at the equator. India, located in the tropical regions, shows high species richness. However, the great Amazon rainforests show maximum biological diversity in terms of the number of species residing in that region. It is believed that in spite of being the region with the highest biodiversity, many species in Amazon are yet to be discovered and identified. The reason for this increased level of biodiversity at the tropics are thought by ecologists to be as follows:
- Tropical areas have a more stable climate compared to that of the temperate areas. As a result, the tropics succeed in supporting a higher number of species as the species do not have to keep adapting to a changing season.
- Temperate regions have suffered a lot of glaciations in the recent past as a result of which they have had a very unstable environment. Whereas, the tropics have been comparatively stable. Thus, speciation has been more favored in the tropics compared to that of the temperate lands.
- The tropical regions are comparatively more susceptible to solar energy. As a result, the plants in this region receive more energy during photosynthesis. This, in turn, transfers more energy to the successive trophic levels in the food chain. Thus, more energy supports more diversity.
- Species-Area relationships – The great German geographer and naturalist, Alexander von Humboldt observed the relation between an area and the species richness found in it. He found that as he increased the area of observation, the plant and animal diversity increased but up to a certain level. Mathematically, it can be explained by the equation
log S = log C + Z log A
S = richness of species
C = Y-intercept
Z = regression coefficient
A = Area
The equation can be represented by the following diagram:
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